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High Slip?

Just took my boat out for the 1st time this year and was trying to test performance from last year after rebuild on carbs and blower.

Boat is a non-notched Cigarette 31' Bullet. Weight should be about 9300-9600lbs with 2 people and about 75 gal of fuel.
Engines are 454's with B&M 250 blowers running 6-7lb boost. Not dynoed, but mechanic tells me 550 or a little more is a good guess for HP.

Boat has 1.5 Bravos in stock location and was spinning 27P Mirages. RPM was at 5200. Max speed with 1-2 foot chop was right at 71 mph by GPS.

After punching in the numbers on the BAM website, it showed a slip of 20-21%. These slip numbers seem high. At the same time, the speed seems low. What could the problem be? I'm thinking of going to 4 blade 26s, but want to find out what's wrong first.

That sounds like a good start. I hade the same problem with a single blown motor deep v, Drop pitch and add blades. Just be easier on it out of the hole, then just slowly roll into the throttles. It worked for me?? Everyone has a liittle differant setup. good luck.

Problem is, I don't think it's just the props. From what I've heard, the early Cigs had a very conservative drive height. Getting on plane quickly is no problem (too much gas will blow out the props, but that's normal), mid-range punch seems OK, and max RPM's are OK. I'm thinking I have another problem....corrosion on lower units (not in real good shape), drives moving around, or something?

Problem is, I don't think it's just the props. From what I've heard, the early Cigs had a very conservative drive height. Getting on plane quickly is no problem (too much gas will blow out the props, but that's normal), mid-range punch seems OK, and max RPM's are OK. I'm thinking I have another problem....corrosion on lower units (not in real good shape), drives moving around, or something?

I'm confused, How did it run last year? is there a lose in performace since the repairs where made? Is there anything in front of the props that could be disturbing the water to the props? 3 blade props usually have a high slip #, 4 blade props would bring that # down.
larry

Last year was the 1st year of running. Engines were not running very well. They would only spin about 4700-4800. Since the boat had been sitting for a couple of years, I had carb and blower rebuilt (one engine would not idle well either). Engines run MUCH better, and I think I'm in the RPM range and have the HP to pull it.

Now that they run as they should, and can pull the current props, I feel the slip is to high, and consequently, the top speed is slightly down. I was wondering what OTHER things can cause a higher slip number.